In a drive shaft of a front-wheel drive vehicle and an independent suspension type rear-wheel drive vehicle, a plunging constant velocity universal joint is used for allowing angular displacement and axial displacement. As illustrated in FIG. 5, the conventional general tripod type plunging constant velocity universal joint includes, as main components, an outer race 110 as an outer joint member, a spider 120 as an inner joint member, and a roller assembly 130 as a torque transmitting element.
The outer joint member 110 includes a mouth portion 112 and a stem portion 116, and a spline (or serration, the same is applied in the following) shaft 118 of the stem portion 116 is coupled to one of two shafts to be connected so as to transmit torque. The mouth portion 112 is cup-like shaped having one open end, and has an inner periphery along which track grooves 114 are formed, a side wall of each of the track grooves 114 serving as a roller guiding surface.
As illustrated in FIG. 6, the spider 120 includes a boss 122 and trunnion journals 126. The boss 122 has a spline hole 124 for being coupled, so as to transmit torque, to the other of the two shafts to be connected. FIGS. 5 and 6 illustrate only one trunnion journal 126. However, for example, three (tripod type) or two (bipod type) trunnion journals 126 are arranged in a circumferential direction of the boss 122 at equal intervals.
Each of the trunnion journals 126 carries the roller assembly 130. Each roller assembly 130 includes a spherical roller 132, needle rollers 134, an inner washer 136, and an outer washer 138. The needle rollers 134 are interposed between an outer peripheral surface of the trunnion journal 126 and an inner peripheral surface of the spherical roller 132 so as to roll therebetween. Therefore, the spherical roller 132 can rotate and axially move with respect to the trunnion journal 126.
The inner washer 136 and the outer washer 138 are arranged at opposite ends in the axial direction of the needle rollers 134. The inner washer 136 has a ring shape, and is interposed between the boss 122 of the spider 120 and end surfaces of the needle rollers 134. The outer washer 138 has an approximately L-shaped cross-section, and includes an axially-extending cylindrical portion 140 and a disk portion 142 extending radially inward from one end portion of the cylindrical portion 140. The other end portion of the cylindrical portion 140 is bent radially outward, and a bent portion 144 has an outer diameter which is larger than an inner diameter of the spherical roller 132. In the vicinity of a tip end of the trunnion journal 126, a peripheral groove 128 is formed. A round circlip 146 is attached in the peripheral groove 128, whereby the movement of the outer washer 138 toward the tip end of the trunnion journal 126 is regulated. Therefore, an inner diameter of the disk portion 142 of the outer washer 138 is smaller than an outer diameter of the round circlip 146. Further, an outer diameter of the cylindrical portion 140 is equal to or smaller than a diameter of a circumscribed circle of the needle rollers 134. Thus, the bent portion 144 of the outer washer 138 prevents the spherical roller 132 from slipping off toward the tip end of the trunnion journal 126.
Aside from the above-mentioned general tripod type plunging constant velocity universal joint, Non-Patent Document 1 describes a tripod type plunging constant velocity universal joint in which the trunnion journal is provided with a flange for receiving the end surfaces of the needle rollers, and the inner washer, the outer washer, and the round circlip are eliminated. That is, as illustrated in FIG. 7, a raceway 128 for the needle rollers 134 is formed along the outer periphery of the trunnion journal 126, and flanges 128a and 128b are formed on opposite ends of the raceway 128. The axial movement of the needle rollers 134 is regulated by the flanges 128a and 128b. In this case, the spherical roller 132 is structured so as to slip off when moving to the tip end portion of the trunnion journal 126. That is, the outer peripheral surface of the trunnion journal 126 has a diameter which is smaller than a diameter of the circumscribed circle of the needle rollers 134 and smaller than a diameter of the inner peripheral surface of the spherical roller 132.
In Patent Document 1, there is proposed provision of the outer washer so as to prevent the slipping off of the spherical roller of the tripod type plunging constant velocity universal joint described in Non-Patent Document 1.
Patent Document 1: JP 2000-510555 A
Non-patent Document 1: Advances in Engineering Series No. 7, “Universal Joint and Driveshaft Design Manual”, (US), The Society of Automotive Engineers, Inc., p. 138